Recently, research on a lithium secondary battery has been actively made, as necessity of a battery having high energy density as a power source for a portable electronic device is increased. In addition, since an electric vehicle and the like is researched with an increasing interest in an environment problem, research on the lithium secondary battery as a power source for the electric vehicle has been actively made.
This lithium secondary battery includes a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes. The separator plays a role of electrically insulating the positive and negative electrodes as well as includes micropores through which lithium ions are transferred.
A separator keeps being required of excellent battery stability due to exothermicity, as a battery tends to be lighter and down-sized and keeps requiring of high capacity as a power source having high power/large capacity for the electric vehicle.
For this battery, a separator formed by coating a binder and a ceramic particle on a porous substrate is mainly used. However, this separator may rarely secure stability due to shrinkage during overheating of the battery.